The Kyushu Region of Southern Japan was affected by a series of Mw 6.0 to 7.0 earthquakes during 14th-16th April 2016, followed by hundreds of aftershocks. The earthquake sequence caused significant damage over a wide area, including Kumamoto City, Mashiki town and the Mount Aso volcanic caldera. In view of valuable lessons to learn from the Kumamoto earthquake sequence, NZSEE selected a team of experienced geotechnical professionals with expertise in geotechnical engineering, engineering geology and associated research for Learning from Earthquakes Mission, and were on the ground between 7th May and 14th May 2016.

The mission was planned in a way that most of the relatively large geographical area that was severely affected by the earthquakes was able to be covered on the ground. This allowed the team to observe and record the type and spatial distribution of the main hazards triggered by the earthquakes. The observations were made only three to four weeks after the main earthquakes, when the government and local authorities were still in the emergency response phase, but after the critical and traumatic phase where the injured and dead had been evacuated. Thus numerous earthquake impacts were observed first-hand by the team, before major repair work that would clear the evidence of damage from the earthquake.

The main types of observed hazard were landslides, ground shaking and surface fault rupture. These landslides mainly comprised earth flows and slides, debris flows and avalanches, earth/debris slides and slumps. Some landslides were reported to have killed at least 10 people out of the 69 confirmed deaths associated with the earthquake. Rupture along the main fault was mapped at the surface over several kilometres.

The earthquake-induced shaking and landslides also caused considerable damage to roads, highways, rail transportation, linear infrastructure (pipes and cables) and high voltage transmission lines. Several bridges, including the critical Aso Bridge, were completely destroyed or were significantly damaged by landslides.

In a few suburbs of Kumamoto City and in Mashiki Town, localised liquefaction took place, causing lateral spreading, differential settlements of the ground and riverbanks, sinking and tilting of buildings, foundation failures, cracks on roads, and disruption of water and sewage pipe networks. The overall effects from liquefaction related hazards, however, appeared relatively minor compared to the damage caused by shaking, landslides and surface fault rupture.

The presentation will provide some discussion about significance of the observations in the context of the potential for earthquake-induced ground damage and consequent damage to the built environment in New Zealand. Such observations can therefore help to identify where similar hazards and impacts could occur in New Zealand, as well as to provide insights on how to mitigate against such hazards.

NZSEE gratefully acknowledges the financial support by the Ministry of Business, Innovation & Employment and EQC for the Learning from Earthquakes programme.

The New Zealand Society for Earthquake Engineering Inc.

A collaborating technical group of the Institution of Professional Engineers New Zealand